Theory of Cascade Induced Forward Raman Scattering in a Plasma

Abstract

Induced forward Raman scattering which proceeds in a cascade fashion in a spatially uniform plasma is considered. Two laser lights, the pump and the first Stokes, are assumed to be incident at time t≥0 on the plasma surface. Their frequencies are much higher than ω_p, the electron plasma frequency, but their difference nearly equals ω_p, and initially the pump has much greater amplitude than the first Stokes. Due to a slight, but finite frequency dependence of the coupling constant between two electromagnetic waves, the electron plasma wave is spatially amplified. This amplification saturates at a relatively low level due to local density depression produced by ponderomotive force of the electron plasma wave. Its amplitude shows a spatial oscillation. The growth length, saturation amplitude and amplitude oscillation length of the electron plasma wave are obtained, as well as the effective absorption length of the pump laser light.